A cDNA library is a collection of cloned DNA molecules propagated in an appropriate host. It is usually derived from the mRNA population of a particular cell, tissue or organ by reverse transcription, cloned into a vector molecule and propagated in an appropriate host cell.
cDNA libraries are useful in numerous applications. cDNA libraries can be used to isolate and identify cell-specific expressed sequences. A cDNA clone isolated from a library can be sequenced and translated (e.g., by computer programs) to derive the primary amino acid sequence of the encoded protein or can be used as a labeled probe to investigate gene expression in vivo.
cDNA libraries can also be used in a two-hybrid assay to screen a large number of candidate proteins and identify those which interact with a particular target protein. In this approach, cDNAs are incorporated into activation domain vectors to provide random proteins fused to an activation domain of a known transcription factor. Vectors encoding the target protein fused to the DNA binding domain of the transcription factor, and the library of activation domain hybrids are cotransformed into a reporter strain. Interaction of the target protein moiety of a target protein DNA binding domain fusion protein with a protein encoded by cDNA brings the DNA binding domain into proximity with the activation domain fused to the cDNA encoded protein. The resulting transcription identifies a positive clone. Once a positive clone has been identified, the gene corresponding to the interacting protein can be isolated and analyzed.
The use of cDNA libraries has become increasingly widespread and, as a result, the need for methods which allow the rapid construction of cDNA libraries in vectors appropriate for particular applications is imperative.